The research proposed in this application is carried out with the objective of obtaiing basic information which can be used to build an understanding in molecular terms of phy siologically important biological membrane phenomena. Work is centered on the continuing investigation of the interactions between lipids in multicomponent bilayers and between lipid and protein components in these systems. Of special interest are multicomponent bilayers exhibiting compositional domain structures wither within the plane of the bilayer or between its apposing faces. The research is specifically aimed at answering the following questions. (1) What factors result in compositionally asymmetric bilayers? (2) What are the properties of bilayers with asymmetric distributions of lipids? (3) What are the conditions governing in-plane compositional domain formation? (4) What are the properties of such systems? (5) What are the factors governing lipid-protein interactions in bilayers? The bilayer systems employed in this work are primarily unilamellar bilayer vesicles of minimum diameter (about 200 Angstrom) and large unilamellar vesicles with diameters greater than 400 Angstrom. Glycerol based lipids are of primary concern. Interactant proteins include cy tochrome b5, the G protein of vesicular stomatitis virus and analogs of this type of intrinsic membrane protein made by semi-synthesis. Assessment of the parameters governing interactions between components and the properties of compositional domain systems will depend upon a variety of physical techniques including fluorescence, NMR (1H, 13C and 31P), photon correlation spectroscopy, differential scanning calorimetry and hy drodynamic methods.